1. Field of the Invention
The present invention relates to a battery pack for supplying power to a portable radiotelegraphic unit, and more specifically, to a battery pack in which a lithium secondary battery is used and charging or discharging of the battery can be effectively controlled according to the detected voltage of the battery.
2. Description of related art
In general, the nickel-cadmium battery (hereinafter called "Ni-Cd battery") is widely used as a battery in a battery pack for a portable radiotelegraphic unit.
Referring to FIG. 1, there is shown a voltage versus time curve of the Ni-Cd battery. As shown in this figure, the discharge characteristic of the Ni-Cd battery is such that the battery voltage remains almost constant for a certain period and then drops abruptly. Due to the nature of the discharge characteristic, the user cannot estimate the residual capacity of the Ni-Cd battery from its voltage. In other word, it is impossible for the user to estimate how long the battery can be used without recharging.
In a conventional battery pack including the Ni-Cd battery, charging and discharging of the battery are repeated alternately regardless of the residual capacity of the battery. As a result, the battery tends to be frequently overcharged or overdischarged, and consequently the life of the battery is often shortened.